A diagram of evolution

Evolution of simple sequence repeats as mutable sites

Because natural selection is commonly presumed to minimize mutation rates, the discovery of mutationally unstable simple sequence repeats (SSRs) in many functional genomic locations came as a surprise to many biologists. Whether such SSRs persist in spite of or because of their intrinsic mutability-whether they constitute a genetic burden or an evolutionary boon--remains uncertain. Two contrasting evolutionary explanations can be offered for SSR abundance. First, suppressing the inherent mutability of repetitive sequences might simply lie beyond the reach of natural selection. Alternatively, natural selection might indirectly favor SSRs at sites where particular repeat-number variants have provided positive contributions to fitness. Indirect selection could thereby shape SSRs into "tuning knobs" that facilitate evolutionary adaptation by implementing an implicit protocol of incremental adjustability. The latter possibility is consistent with deep evolutionary conservation of some SSRs, including several in genes with neurological and neurodevelopmental function.

Cyril Dean Darlington: the man who 'invented' the chromosome

Cyril Darlington (1903-1981) was the most famous cytologist in the world in the decades preceding the molecular revolution of the 1950s. He crossed disciplinary boundaries to create a synthesis of cytology, genetics and evolution by revealing the mechanics of chromosomal recombination and the importance of its evolution. Always controversial during his lifetime, obituaries ultimately referred to him as the 'Copernicus' or 'Newton' of cytology. This article reviews Darlington's scientific contributions, the reasons for their difficult reception at the time and their continuing relevance.

Phylogenesis of fission yeasts. Contradictions surrounding the origin of a century old genus

The phylogenesis of fungi is controversial due to their simple morphology and poor fossilization. Traditional classification supported by morphological studies and physiological traits placed the fission yeasts in one group with ascomycetous yeasts. The rRNA sequence comparisons, however, revealed an enormous evolutionary gap between Saccharomyces and Schizosaccharomyces. As shown in this review, the protein sequences also show a large gap which is almost as large as that separating Schizosaccharomyces from higher animals. Since the two yeasts share features (both cytological and molecular) in common which are also characteristic of ascomycetous fungi, their separation must have taken place later than the sequence differences may suggest. Possible reasons for the paradox are discussed. The sequence data also suggest a slower evolutionary rate in the Schizosaccharomyces lineage than in the Saccharomyces branch. In the fission yeast lineage two ramifications can be supposed. First S. japonicus (Hasegawaea japonica) branched off, then S. octosporus (Octosporomyces octosporus) separated from S. pombe.